the pH values of the analyte at many different points not just the point at

The ph values of the analyte at many different points

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the pH values of the analyte at many different points, not just the point at which it reaches the equivalence point. Thus, potentiometry is often used for dilute solutions. Because the endpoint is indicated at the largest potential break, the exact potential is unnecessary and only the change in cell potential is needed. Also, the glass electrode does not need to be calibrated with a standard buffer nor does the pH meter need to be a high-end model since potential need not be read closely. However, in order to anticipate the endpoint, so that one will add smaller increments as it begins to neutralize, the approximate equivalence point may be predetermined using calculations, volumetric titrations or a run of potentiometric titration. Aside from the concentration of the sample, its acid-dissociation constant (Ka) and percent purity was also determined. Three trials were done using a pH meter set-up as described in Figure 1. 1
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Figure 1. Set-up for Potentiometric Titration The pH meter’s electrode is immersed in the beaker containing the analyte while it is titrated with a NaOH solution. The magnetic stirrer was used so that the solution is constantly mixed and the NaOH is equally distributed throughout the analyte, Potassium Hydrogen Phthalate (KHP). At each addition of titrant, the pH was recorded and was used to determine the equivalence point, acid- dissociation constant and percent purity. For the first run, the solution was added 50 ml of titrant. For each pH recording, 1 ml of titrant was added. The approximate endpoint determined in the first run was used in the following runs so that the complete neutralization can be anticipated and smaller increments can be added as it reaches the endpoint. However, the volume increments should not be too small as
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  • Fall '17
  • Sir Jaden Smith
  • pH, potentiometric titration

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